Excel =Date and Leap Years

Perhaps you need to reconsider exactly where you're adding the time.

The DATE function will behave as you suggest if you add the time to the day portion:

=date(year(A1), month(A1), day(A1) + B1*365 + B2*30)

But you'll need to seriously consider the error you are incorporating, especially when you want to add a "standard" month of 30 days.

Cheers,